#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
using namespace std;
#include <vector>

int main() {
    int h = 0;
    int w = 0;
    cin >> w >> h;
    vector<vector<int>> arr(w, vector<int>(h, 0));
    int count = 0;
    for (int i = 0; i < w; i++)
    {
        for (int j = 0; j < h; j++)
        {
            if (arr[i][j] != 2)
            {
                arr[i][j] = 1;
                count++;
                if (i + 2 < w)
                {
                    arr[i + 2][j] = 2;
                }
                if (j + 2 < h)
                {
                    arr[i][j + 2] = 2;
                }
            }

        }
    }
    cout << count;

}